The death toll in the Boston Marathon bombings has increased to three people, according to the Boston Police commissioner.

Among the dead was an 8-year-old boy, law enforcement sources told ABC News.

“This cowardly act will not be taken within stride,” Boston Police Commissioner Ed Davis said this evening. “We will turn every rock over to find the people who are responsible for this.”

At least 140 people were injured, including several children with severe trauma, when bombs exploded almost simultaneously near the marathon finish line, police said.

No one has claimed responsibility for the explosions.

WJON reports former Minnesota State Representative Larry Hosch of St. Joseph ran in Monday’s Boston Marathon. He says he finished the race before the explosions happened, and he and his family are all okay. He says communication by cell phone was difficult.

Tim Wright of Sauk Rapids, Minnesota and another local runner were near the finish line area when two explosions went off. Wright and fellow Sauk Rapids runner Liz Watland were changing into dry clothing when the bombs detonated. They were not hurt. They say they heard the explosion and then saw a ploof of smoke.

Their spouses were in the food court, which is very near the area where the bombs went off, at the time of the explosion but neither were hurt.

President Barack Obama said after the incident, “We still do not know who did this or why. And people shouldn’t jump to conclusions before we have all the facts. But make no mistake — we will get to the bottom of this. And we will find out who did this; we’ll find out why they did this. Any responsible individuals, any responsible groups will feel the full weight of justice.”